© National Instruments Corporation 1-1 GPIB-100A User Manual
Chapter 1Description of the GPIB-100A

Introduction

The high-speed GPIB-100A Bus Extender (Figure 1-1) is used in pairs with a special parallel data
transmission cable to connect two separate GPIB or IEEE-488 bus systems in a functionally
transparent manner.
Figure 1-1. The Model GPIB-100A Bus Extender
While the two bus systems are physically separate, as shown in Figure 1-2, devices logically
appear to be located on the same bus as shown in Figure 1-3. Thus, with the GPIB-100A it is
possible to overcome two configuration restrictions imposed by ANSI/IEEE Standard 488-l978,
namely:
• Cable length limit of 20 m total per contiguous bus or 2 m times the number of devices on the
bus, whichever is smaller.
• Electrical loading limit of 15 devices per contiguous bus.
Each GPIB-100A system extends the distance limit by 300 m and the loading limit to 30 devices
including the extenders, without sacrificing speed or performance. These point-to-point extender
systems can be connected in series for longer distances or in star patterns for additional loading.
At short distances, the data transfer rate over the extension can exceed 250 kbytes/sec, degrading
with distance only by the propagation delay along the cable. Furthermore, regardless of the
distance, there is no speed degradation at all for transfers between devices on the same side of the